1. Field of the Invention
The present invention relates to a process for modifying surface of nitride and to nitride having surfaces modified by such process, and more particularly, to a process for irradiating energized ion particles onto the nitride surface, while blowing a reactive gas directly over the nitride surface, under a vacuum condition in order to decrease a wetting angle of the nitride surface and to increase an adhesive strength thereof.
2. Description of the Conventional Art
The wetting angle is an important factor in identifying the condition of a material surface which has been modified. A decrease in wetting angle implies that a polymer surface attracts water and also implies that the surface exhibits hydrophilicity. Thus, the occurrence of a spreading phenomenon increases when an aqueous dyestuff is applied on such a polymer surface, adhesive strength with other materials increases, and light scattering generated by condensation of water in the air onto the surface is inhibited. As described above, the surface condition of a polymer can be modified by decreasing the wetting angle.
In general, changes in wetting angle have been achieved by (1) surface roughening, (2) surface cleaning, (3) providing a coating with hydrophilic functional groups, and (4) directly synthesizing the surface with hydrophilic functional groups, while increases in adhesive strength are achieved by methods similar to those used for changing the wetting angle, namely (1) forming chemical linkages between the two materials to be adhered, (2) surface cleaning, (3) applying a material which is adhesive to the materials to be adhered, and (4) forming the surface with functional groups for assisting chemical bonds with the materials to be adhered (mainly hydrophilic functional groups).
In particular, examples of processes currently used for decreasing the wetting angle in modifying polymer surfaces include surface synthesizing with hydrophilic functional groups, high voltage corona discharge and direct current plasma discharge.
Among these, high voltage corona discharge is a process in which a polymer sample is placed in a vacuum chamber into which a reactive gas or gases are filled until atmospheric pressure is reached and then the sample is ionized by electrons emitted from electrodes to form a plasma having negative ionic charges and positive ionic charges in an electromagnetic amount equal to that of their electrons (hereinafter, referred to as "cold plasma"), and the reactive gas ions thusly formed are reacted with the sample surface to modify the surface thereof. Although this process is most widely used in modifying polymer surfaces, as disclosed in Japanese Laid-Open Patent Publication No. 60-13823 (Jan. 24, 1985), only a process of treating the surface of vinyl chloride with chlorine gas under atmospheric pressure by the use of high voltage corona discharge is disclosed, in which the wetting angle was decreased from 73.degree. to 32.degree., and this decrease of wetting angle was not prominent.
Although the process is similar to that of high voltage corona discharge, direct current plasma discharge uses a plasma generated through a glow discharge (referred to as a "thermal plasma"), i.e., an ionized reactive gas or gases, which is formed after charging a reactive gas or gases in a vacuum chamber under 0.01-5 torr (atmospheric pressure is 760 torr). However, this process does not exhibit a sufficient effect in decreasing the wetting angle. For example, Japanese Laid-Open Patent Pub. No. 61-171740 (Aug. 2, 1985) discloses that the wetting angle measured after modifying the surface of polymethyl methacrylate (PMMA) polymer in argon gas under a pressure of 0.1 torr was found to be 40.degree., and the wetting angle increased to 60.degree. after washing the PMMA polymer surface several times with water. Further, the wetting angle measured after modifying the surface of BX3 polymer under a pressure of 0.1 mbar (atmospheric pressure is 1013 mbar) in an oxygen gas atmosphere was found to be between 48.degree. to 20.degree., when treated with an applied voltage of 10-100 W for 160 seconds [D. W. Fakes, J. M. Newton, J. F. Wattes and M. J. Edgell, Surface and Interface Analysis, vol.10 416-423(1987)].
The conventional processes, as mentioned above, cannot significantly decrease the wetting angle, whereby the effects of spreading aqueous dyestuffs on polymer surface, increasing the surface adhesive strength with other polar materials, and inhibition of light scattering because of water condensation from the air are insufficient. In addition, if the wetting angle is decreased using conventional techniques, the change in the wetting angle tends to approach a certain value according to an increase in time for surface modification, as in the case of Teflon (R) (PTFE), whereby the wetting angle with water is changed from about 95.degree. to about 50.degree. when using hydrogen plasma [D. T. Clark and D. R. Hutton, J.Polym. Sci., Part A, 25, 2643(1987)] or is changed from about 110.degree. to about 70.degree. when using a water steam plasma [D. Yousian and H. J. Griesser, Polymer, 32(6) 1126(1987)].
The present invention allows modification of material surfaces by irradiating energized ion particles onto the surfaces of a polymer, ceramic, ITO or glass, while blowing reactive gas or Cases directly over the material surface under a vacuum condition.